Heat recovery system

ABSTRACT

The invention relates to a heat recovery system. Said system comprises a heat recovery device having a plurality of heat recovery plates; a fluid supply means connectable to at least the heat recovery device. The heat recovery device is operable to supply a fluid at a first temperature to the fluid supply means; and a refrigeration assembly. The refrigeration assembly is operable to supply a fluid to the heat recovery device at a second temperature.

The invention relates to an improved heat recovery system. The inventionfurther relates to an improved heat recovery device for use in the heatrecovery system.

Most buildings, whether they are for commercial or domestic use, need asupply of hot water. For example, the hot water may be needed for use incentral heating systems, washing machines, or dishwashers. Commonly, ahot water tank is provided in a building to store water and heat it totemperatures in the region of 70° C. When a portion of the hot water isrun off for use in an appliance, this water is replaced in the tank bycold water, often mains cold water, which is generally at around 10° C.The effect of adding cold water to the hot water tank is to cause animmediate reduction in the temperature of the water already present. Tocompensate, hot water tanks generally comprise a heat source which istriggered to heat the water. In normal use, the water may be reheated anumber of times each day in order to maintain an elevated temperature.Consequently, the system consumes a large amount of heat energy. Thus,known systems are inefficient and expensive to operate.

Many kitchens, in particular, commercial kitchens, generate a largeamount of heat energy during cooking. Often, this heat energy, or hotfluid flow, dissipates into the environment, or is directed away fromthe kitchen through an exhaust or dirty air outlet.

It is an object of the invention to provide a heat recovery system whichis energy efficient and economical to operate. It is a further object ofthe invention to provide a heat recovery device for use in the heatrecovery system.

According to an aspect of the present invention there is provided a heatrecovery system comprising a heat recovery device having a plurality ofheat recovery plates; a fluid supply means connectable to at least theheat recovery device; the heat recovery device being operable to supplya fluid at a first temperature to the fluid supply means; and arefrigeration assembly, the refrigeration assembly being operable tosupply a fluid to the heat recovery device at a second temperature.

Preferably, the heat recovery plates are mounted substantially parallelto each other.

Preferably, the fluid is an exhaust airflow, preferably a hot exhaustgas. The fluid may be water.

Preferably, the heat recovery device is located in a dirty exhaust duct,preferably an exhaust duct from a kitchen, most preferably a commercialkitchen. The heat recovery device may be located in a flue of a boiler.

The heat recovery device operates substantially in the manner of a heatexchanger, by transferring heat through a conducting wall, i.e. saidheat recovery plates, from one fluid to another.

Preferably, the heat recovery device comprises a fluid inlet and a fluidoutlet. Preferably, fluid in the fluid outlet is at a temperaturegreater than fluid in the fluid inlet. Preferably, the refrigerationassembly is located between the fluid inlet and the fluid outlet.

Preferably, the refrigeration assembly is an inverter drivenrefrigeration assembly. Preferably, said assembly comprises acompressor, preferably an inverter compressor. Said compressor isoperable to continuously operate and may speed up if the temperature ishigher than needed or slow down if the temperature is too low.

Preferably, a refrigerant is circulated through the refrigerationassembly. Preferably, the refrigerant is a HFC refrigerant, mostpreferably R404a.

Unlike conventional compressors that start or stop repetitively, aninverter compressor provides finely tuned operation with reducedtemperature variations. In so doing, the power consumption of aninverter compressor is lower than known standard compressors.

Preferably, the refrigeration assembly comprises at least one plate heatexchanger. Preferably, the or each plate heat exchanger is operable toexchange heat energy from the refrigerant to the fluid. Preferably, twoplate heat exchangers are provided. Preferably, a first said exchangeris operable to cause heat exchange between the refrigeration assemblyand the heat recovery device. Preferably, a second said exchanger isoperable to cause heat exchange between the refrigeration assembly and aheat exchange system of a dwelling, preferably a hot fluid system of adwelling. Preferably, the refrigeration assembly, preferably the secondplate exchanger is operable to provide a substantially continuous supplyof fluid at an elevated temperature to a dwelling.

Preferably, the exhaust air flowrate is between substantially 0.5 and100 m³/s, most preferably substantially between 2 and 10 m³/s, mostpreferably 3 m³/s. Preferably, the refrigerant flowrate is betweensubstantially 0.1 and 1 kg/s, most preferably substantially 0.26 kg/s.

Preferably, the fluid is a liquid, preferably comprising a refrigerantand a liquid, most preferably glycol and water. The fluid may be a gas.

Preferably, the first temperature of the fluid is greater than thesecond temperature of the fluid.

Preferably, the fluid is re-circulated through the heat recovery device.Preferably, the refrigerant is re-circulated through the refrigerationassembly.

Preferably, the fluid supply means supplies fluid to a holding tank,preferably at a temperature greater than the mains cold watertemperature. Preferably, the fluid in the tank is at a temperature ofsubstantially between 50° C. and 100° C., most preferably substantiallyat 70° C.

Preferably, the heat recovery system further comprises a buffercylinder. Preferably, the buffer cylinder is located downstream of theheat recovery device. Preferably, the buffer cylinder is upstream of thetank. Preferably, the buffer cylinder is operable to store fluid fromthe heat recovery device. Preferably, the buffer cylinder is operable tosupply fluid for use by a user or in an appliance. Preferably, thebuffer cylinder is operable to supply fluid at an elevated temperatureto the tank.

Preferably, at least one valve is provided in the heat recovery system.Said valve may be operable to release fluid from the tank. Said valvemay be operable to release fluid from the buffer cylinder.

Preferably, communication means are provided being operable tocommunicate to the at least one valve to cause said valve to open orclose.

Preferably, when an amount of fluid is released from the tank, the fluidsupply means is operable to supply an equal amount of fluid to the tank.In this manner, the tank is kept at substantially a constant level.Further, because the fluid supplied to the tank is at an elevatedtemperature, the temperature of the fluid in the tank is substantiallymaintained. Preferably, the fluid is supplied from the buffer cylinder.

Preferably, a temperature measurement means is provided in the heatrecovery system, preferably in the tank. Preferably, the temperaturemeasurement means is operable to communicate with a heating system forthe tank. Preferably, the heating system is operable to switch on/off,preferably depending on the temperature of the fluid in the tank.

Preferably, the heat recovery device is at a temperature greater thanthe temperature in the buffer cylinder.

In this manner, the heating system, for example, an immersion heater, isonly switched on when the temperature of the fluid in the tank drops toa predetermined value. For example, the immersion heater will not betriggered to switch on until the fluid in the tank reaches 60° C.

Preferably, the tank is operable to supply fluid at an elevatedtemperature, preferably, to an appliance, preferably a dishwasher, orwashing machine. The tank may supply said fluid to a central heatingsystem. Advantageously, the water supply means provides water at atemperature greater than mains cold water to the tank. In so doing, thetemperature of the fluid in the tank is maintained at an elevatedtemperature, preferably 70° C.

The system provides a means of maintaining the temperature of the tankwater without having an additional heat source, for example, a heatingcoil or heat exchanger within the tank. Advantageously, the system cansave approximately substantially between 2 and 100 Kw and is thereforeeconomical and efficient.

Preferably, seven heat recovery plates are provided in the heat recoverydevice. Preferably, said plates are mounted perpendicular to a duct.

Preferably, at least one heat recovery plate comprises a wall of theduct.

Preferably, each said plate comprises a pair of plate members. Saidmembers preferably being welded together. Most preferably, the membersare welded together along a weld line which is located adjacent theperiphery of at least one of said members. Preferably, the weld line isspaced substantially between 5 mm and 15 mm from said periphery, mostpreferably substantially 10 mm.

Preferably, the members are alternatively or preferably additionallywelded along a line which is located substantially centrally of saidmembers. Preferably, the central weld line extends from one side of themembers towards an opposite side. Preferably, the weld line extendssubstantially parallel to a top or bottom edge of the plates.Preferably, the members are welded at a plurality of points across thesurface thereof. Preferably, the plurality of weld points areequi-distantly spaced apart, preferably being substantially between 35mm and 55 mm apart, preferably substantially 45 mm apart from eachother. Preferably, the or each weld point is oval in cross section. Mostpreferably, each weld point is tear-drop shaped in cross section,preferably in plan view.

Advantageously, the plurality of welded points are laser welded.

The weld points ensure that fluid passing through the members is evenlydispersed. Further, it has been shown that a weld point having atear-drop cross section is highly advantageous. Specifically, such aweld point eliminates “hot spots” on the recovery device. As a result,there is a surprising advantageous effect that a constant heat recoveryresults.

Preferably, the heat recovery plate comprises two members being laserwelded along a periphery, and being welded at a plurality points on thesurfaces thereof. Preferably, said members have substantially equalcross sectional area. The first member may be thicker than the secondmember. Preferably, the first and second member may be of equalthickness. Preferably, the first member comprises a lower layer and thesecond member comprises an upper layer of the plate.

Preferably, the heat recovery plate is substantially rectangular in planview. Preferably, said plate is substantially between 100 and 500 cm inlength and substantially between 30 cm and 100 cm in width. Mostpreferably, said plate is substantially 200 cm by 70 cm in dimension.Preferably, the heal recovery plate comprises an inlet and preferably anoutlet. Preferably, the inlet and/or the outlet are each substantiallybetween 15 and 30 mm in diameter. Preferably, the inlet diameter issubstantially equal to the outlet diameter, preferably each diameterbeing substantially 22 mm. Preferably, the inlet and outlet are spacedapart by preferably substantially between 20 and 70 cm, preferablysubstantially 36 cm.

Preferably, the heat recovery device, preferably each said plate, ismanufactured from metals, preferably stainless steel.

The heat recovery device may be positioned adjacent a cooking appliance,preferably a cooker hood. The heat recovery device may be positioned inthe canopy of a cooking appliance, preferably an industrial cookingappliance. The heat recovery device may form part of a splash-back to acooking appliance.

All of the features described herein may be combined with any of theabove aspects, in any combination.

An embodiment of the invention wilt now be described, by way of exampleonly, with reference to the accompanying drawings, wherein:

FIG. 1 shows a schematic perspective view of a heat recovery deviceaccording to the invention;

FIGS. 2 a and 2 b show a schematic side view and plan view respectivelyof a heat recovery device according to the invention;

FIGS. 3 a and 3 b show a schematic side view and plan view respectivelyof a heat recovery device according to the invention;

FIG. 4 shows a schematic side sectional view of a heat recovery deviceaccording to the invention;

FIG. 5 shows a schematic side sectional view of a heat recovery deviceaccording to the invention;

FIG. 6 shows a schematic perspective view of a heat recovery deviceaccording to the invention;

FIGS. 7 a, 7 b and 7 c show a schematic plan view, an exploded schematicplan view, and a schematic side view respectively of a heat recoverydevice according to the invention;

FIGS. 8 a, 8 b, 8 c and 8 d show a schematic plan view, an explodedschematic plan view, a schematic side view and a schematic side viewrespectively of a heat recovery device according to the invention;

FIG. 9 shows a schematic layout of a heat recovery system according tothe invention;

FIG. 10 shows a schematic layout of an embodiment of a heat recoverysystem according to the invention; and

FIGS. 11 a, 11 b and 11 c show a schematic perspective view ofalternative embodiments of a heat recovery device according to theInvention.

FIG. 1 shows a part of a heat recovery system 2 according to theinvention. The system 2 comprises a heat recovery device 4 comprisingseven heat recovery plates 6, and a refrigeration assembly 8. Therefrigeration assembly 8 comprises an inverter compressor 10, fans 12,and a heat exchanger plate 14. A dotted line is shown in the figure,dividing the heat exchanger plate 14 into section A and section B forease of reference. Fluid supply means 16 are provided to connect theheat recovery device 4 and the refrigeration assembly 8. The fluidsupply means 16 comprise an outlet 18 from the heat recovery device 4and an inlet 20 to the heat recovery device 4. An expansion valve 22 isprovided on the inlet 18. A low pressure hot water pump 24 is providedon a water outlet 26.

FIGS. 2 a and 2 b show the heat recovery plate 6 for use in the system2. The heat recovery device 4 is generally rectangular in plan view andcomprises a first member 30 and a second member 32. The first member 30is arranged to be a lower layer or surface and the second member 32 isarranged to be an upper layer or surface. The second member 32 isthinner than the first member 30. It can be seen from FIG. 2 b that themembers 30, 32 are welded together around a periphery 34. It has beenfound that laser welding is advantageous in comparison to spot weldingtechniques. This is because laser welding achieves stronger weld points,and a large volume of plates can be welded during the welding process,making the process quicker than spot welding. The welded points 36 arelocated across the members 30, 32, together with a central weld line 38.An inlet 40 and an outlet 42 are located on the members 30, 32 towards afirst end 44. The welded points 36 will be discussed in further detailbelow. FIGS. 3 a and 3 b show an alternative embodiment of a heatrecovery plate 104. The plate 104 is elongated in comparison to thedevice 4.

FIGS. 4, 5 and 6 show a sequence of steps for the manufacture of theplate 4, 104. in a first step, the two members 30, 32 are weldedtogether around the periphery 34. The surface of the members 30, 32 isthen laser welded at a plurality of point 36. Gas, preferably nitrogen,is then passed through the sandwiched members 30, 32 as shown in FIG. 4.Due to the second member 32 being manufactured from thinner materialthan the first member 30, the second member 32 buckles or bubblesupwards by the force of the gas as shown in FIG. 5. FIG. 6 shows aperspective view of the resultant surface of the second member 32. Inthis arrangement, fluid entering the plate 4 is channelled over a largesurface area due to the bubbled effect. Advantageously, this provides amaximum area for heat exchange to occur. FIGS. 7 a and 7 b show the heatrecovery plate 204 in greater detail. In this embodiment, the weld line238 extends to a point adjacent the periphery 234. The rise of eachbubble in the second member 232 is approximately 3 mm.

FIGS. 8 a to 8 c show an alternative embodiment of the heat recoveryplate 304. In this embodiment, three laser welded lines 338 are providedon the members 330,332. FIG. 8 d shows a preferred arrangement of saidmembers in which both sides of the heat recovery plate 304 is “bubbled”or raised. This is achieved by both members being of equal thicknesssuch that when nitrogen is passed between them, inflation occurs on bothsides which results in the increase in surface area.

In use, hot exhaust gas flows through the heat recovery device 4 asindicated by the arrow in FIG. 1. Heat exchange occurs as the hot gaspasses over the cooler plates 6. Fluid exits the device 4 via the outlet18 and passes through the compressor 8 to the plate heat exchanger 14.On the side labelled UK, the fluid from the heat recovery device 4circulates to allow heat exchange to occur across the exchanger 14.Fluid leaving the exchanger 14 is thus at a lower temperature and isdirected to the compressor 8 to be cooled further. The cooler fluid thenre-enters the heat recovery device 4 to begin heat exchange with theexhaust flow again. Side “B” of the figure shows heat transferred fromthe fluid flow into the exchanger 14 is directed to the dwelling flow tocreate a hot fluid flow for use in, for example, a water tank. Flowleaving the dwelling is then directed back to the exchanger 14 to beginheat exchange once again.

FIG. 9 shows a schematic of the heat recovery system 2. For ease ofunderstanding, the system 2 can be split into three sections, namelysections X, Y and Z as shown in the figure. The operation of the system2 is as follows.

Section X comprises the heat recovery device 4. In use, hot fluid,particularly hot dirty air exhaust, flows into the heat recovery device4 and over the plates 6. A refrigerant fluid, preferably a water/glycolmix of fluid, circulates through the plates 6 to provide a suitableenvironment for heat exchange to occur between the hot exhaust flow andthe water/glycol mix. The refrigerant fluid exits the device 4 viaoutlet 18. The fluid is at an elevated temperature due to heat exchange.The fluid is directed to a first plate heat exchanger 50 of therefrigeration system 12. A refrigerant gas circulates through therefrigeration system 12, preferably R404a, and causes heat exchange tooccur between the refrigerant liquid and refrigerant gas such that therefrigerant liquid temperature is decreased. The low temperaturerefrigerant liquid is directed back through the inlet 20 to the heatrecovery device 4.

Section Y comprises the refrigeration system 12. Fluid at an increasedtemperature leaves plate heat exchanger 50 and is directed into thecompressor 10 and towards plate heat exchanger 52. The fluid at elevatedtemperature leaves heat exchanger 52 to be directed to a hot water orheating system of a dwelling in section Z. Heat exchange occurs at theplate heat exchanger 52 such that fluid at a lower temperature isreturned to the compressor 12 and to the plate heat exchanger 50 to takepart in heat exchange for section X.

Section Z is the “hot” fluid section of the system 2. Section Zcomprises a heater battery 60, fan coils 62, a door heater 64 and a hotwater tank 66. Fluid exiting the plate heat exchanger 52 is at anelevated temperature and so can be supplied to, for example, the heaterbattery. The fluid in section Z is them directed back to the plate heatexchanger 52 to again allow for heat exchange to occur.

The system of the invention may also be used in “summer conditions” whena dwelling requires cooling for air conditioning. An example of such asystem 200 is shown in FIG. 10. it will be understood be the reader thatlike numerals to like parts to those used in FIG. 9 are used. Aplurality of three way valves 270 are incorporated into the system 200to allow a user to direct a low temperature fluid flow to, for example,the fan coils 262. Further, the user can choose to direct the flow topromote heat exchange to provide hot water to the tank 266. The systemallows for both cooling of the dwelling and also provides hot water tothe dwelling.

FIG. 11 a shows an embodiment of the heat recovery device 4. The heatrecovery plates 6 may be sized according to the building application,being orientated vertically or horizontally as show in FIGS. 11 a and 11b. or forming at least a section of the duct itself as shown in FIG. 11c.

The system is particularly suitable for the recovery of waste heat fromkitchen extract air in a commercial kitchen. A refrigerant is used topromote heat transfer. The refrigerant may be R22 but R404a ispreferred. In test conditions, the waste air flow rate was 3 m³ /s andrefrigerant flow rate 0.26 kg/s. The total recovered heat from the wasteair to the refrigerant was predicted to be 23.8 kW, of a total availableheat 72.4 kW, achieving a heat recovery performance of 33%, relative toambient air temperature 10 deg-C. Furthermore, the heat exchangerperformance as an evaporator achieved a refrigerant vapour quality of63%.

The system may comprise a number of heat recovery devices, beinginstalled within the extracted air stream. The number of heat recoverydevices installed is based around the building heating requirements andthe amount of wasted energy the dwelling discharges into the atmosphere.The evaporator (a number of plate heat exchangers) is sized inconjunction with a refrigeration system which delivers the optimum flowrate of refrigerant through the plates to absorb the waste heat energy.

Due to the system lowering the surface plate temperature below the dewpoint, this causes condensation to form upon the surface of the plates.This in turn increases the heat transfer and also reduces the amount ofgrease forming on the surface of the plate. A conventional heat recoverysystem cannot be used due to grease clogging up the face of the coilswhich could potentially be a fire hazard and cause mechanical failure.The refrigeration system is designed and sized to operate around theevaporator and plate heat exchanger requirements. The compressor isinverter driven and controlled to optimise energy saving as thebuildings heating and cooling demand is not fixed, therefore in thewinter period the heating demand to the building is greater than insummer. Each refrigeration system and evaporator is designed to relateto the buildings heat loss, water heating and the buildings coolingrequirements, but on some occasions full heat recovery is achieved andthe surplus energy can be stored for further or future use. Therefrigeration system has an air cooling condenser which is used when theplate heat exchanger requires assistance following a low heating demandto the building; meaning the refrigerant requires further heat loss tocondense the gas to a liquid. Again these fans are speed controlled tooptimize energy savings. The refrigeration system is used to cool thebuilding in summer and in summer the buildings heating is not requiredbut other items require heat (i.e. hot water requirements). Therecovered heat from the cooling process will generate the buildingsheating requirements during summer. In this period recovering the heatfrom the dirty extracted air may not be required as the buildingscooling load may generate sufficient heating. The refrigerant for theprocess is designed specifically to suit the buildings individualrequirements. Selecting the refrigerant is based around the performance,efficiency and current regulations. When selecting the refrigerant andthe equipment we look at the COP (coefficient of performance) as thesystem is an energy saving application the operating costs associatedare very important. The plate heat exchanger is sized to optimise theheat transfer for the refrigerants heat rejection from the evaporator tothe fluid flow and return network (Low pressure hot water). The LPHWsystem can be connected to a number of appliances, heating fan coils,over door heater, hot water cylinder etc. The water side of the plateheat exchanger can not only be sized for the refrigerant side but alsothe fluid side to suit appliances optimum flow rates.

The reader's attention is directed to all papers and documents which arefiled concurrently with or previous to this specification in connectionwith this application and which are open to public inspection with thisspecification, and the contents of all such papers and documents areincorporated herein by reference.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed.

1-25. (canceled)
 26. A heat recovery system comprising a heat recoverydevice having a plurality of heat recovery plates; a fluid supply meansconnectable to at least the heat recovery device; the heat recoverydevice being operable to supply a fluid at a first temperature to thefluid supply means; and a refrigeration assembly, the refrigerationassembly being operable to supply a fluid to the heat recovery device ata second temperature.
 27. A heat recovery system as claimed in claim 26,wherein the heat recovery plates are mounted substantially parallel toeach other.
 28. A heat recovery system as claimed in claim 27, whereinthe fluid is a hot exhaust gas.
 29. A heat recovery system as claimed inclaim 28 wherein the heat recovery device is located in an exhaust duct.30. A heat recovery system as claimed in claim 29, wherein the heatrecovery device comprises a fluid inlet and a fluid outlet.
 31. A heatrecovery system as claimed in claim 30, wherein fluid in the fluidoutlet is at a temperature greater than fluid in the fluid inlet.
 32. Aheat recovery system as claimed in claim 31, wherein a refrigerationassembly is located between the fluid inlet and the fluid outlet.
 33. Aheat recovery system as claimed in claim 32, wherein the refrigerationassembly is an inverter driven refrigeration assembly.
 34. A heatrecovery system as claimed in claim 33, wherein said assembly comprisesan inverter compressor.
 35. A heat recovery system as claimed in claim34, wherein a refrigerant is circulated through the refrigerationassembly, the refrigerant being R404a.
 36. A heat recovery system asclaimed in claim 35, wherein the refrigeration assembly comprises atleast one plate heat exchanger.
 37. A heat recovery system as claimed inclaim 36, wherein two plate heat exchangers are provided, a first saidexchanger being operable to cause heat exchange between therefrigeration assembly and the heat recovery device.
 38. A heat recoverysystem as claimed in claim 37, wherein a second plate heat exchanger isoperable to cause heat exchange between the refrigeration assembly and aheat exchange system of a dwelling.
 39. A heat recovery system asclaimed in claim 38, wherein the exhaust air flowrate is betweensubstantially 0.5 and 100 m³/s.
 40. A heat recovery system as claimed inclaim 39, wherein the exhaust air flowrate is substantially 3 m³/s. 41.A heat recovery system as claimed in claim 40, wherein the refrigerantflowrate is between substantially 0.1 and 1 kg/s.
 42. A heat recoverysystem as claimed in claim 41, wherein the first temperature of thefluid is greater than the second temperature of the fluid.
 43. A heatrecovery system as claimed in claim 42, wherein the fluid isre-circulated through the heat recovery device.
 44. A heat recoverysystem as claimed in claim 43, wherein seven heat recovery plates areprovided in the heat recovery device.
 45. A heat recovery system asclaimed in claim 44, wherein said plates are mounted perpendicular to aduct.